There are many known processes for welding, and each process has strengths and weaknesses. Users generally select the type of process based on characteristics of the welding job, such as speed, quality, environment, material to be welded, etc.
One well known process is submerged arc (sub arc) welding, which involves the arc being submerged beneath flux. The arc is established between a consumable electrode and the workpiece and moves along a weld path. Flux is deposited along the work path ahead of the arc and the flux (and the workpiece along the weld path) is melted by the heat of the arc. Sub arc welding is known for high deposition (a large amount of flux is melted) but not all of the flux is used, and cleaning the slag and excess flux after the weld is completed takes time and can be troublesome. Also cleaning the slag requires a wider groove, typically an angle of about 50 degrees. Sub arc welding has been used to deposit 30 pounds per hour on high current welding.
Another known process is MIG welding. MIG welding is typically performed with dc and involves a consumable electrode (wire) being fed to the arc. The arc melts the wire along the weld path. MIG welding is not as fast as sub arc welding, but does not have the excess flux to be cleaned that sub arc has. DC MIG welding has been known to deposit 17–20 pounds per hour. The arc plasma column in dc MIG may cause the arc to dig or tunnel excessively and ultimately produce lower quality welds if an attempt is made to use greater deposition rates.
DC MIG welding systems can be relatively low cost, because they can have simple power circuits. MIG welding (or GMAW), as used herein, includes an arc welding process which joins metals by heating them with an arc. The arc is between a continuously fed filler metal (consumable) electrode and the workpiece. Externally supplied gas or gas mixtures provide shielding. MIG welding often is performed by welding along a weld path that is a groove along the workpieces to be joined.
MIG has typically been performed using dc current. AC current is rarely used in part, because the ac MIG process can be difficult to maintain through a zero crossing—the current must pass through zero at the end of each half cycle, and this can cause the MIG arc to extinguish.
Some prior art systems have used an inverter for ac MIG welding, which can have very rapid zero crossings, thus helping to stabilize the arc. However, inverters can be expensive, particularly at higher currents. Such prior art systems have not been able to deposit as much material as dc MIG systems.
The composition of the wire affects the ability of the system to maintain the arc during zero crossing. The wire may be flux cored, or metal cored. Many prior art wires exacerbate the zero crossing problem in ac MIG welding.
Accordingly, a welding system that is as fast as, or faster than, a sub arc system, but does not have the drawbacks of a sub arc system, is desirable. Preferably the groove on the workpieces to be welded may be narrow, to facilitate faster and better welds. Also, a wire that is suitable for ac MIG welding is desirable.